why html includes six levels of headings but not many more ?

Answer 1

it would be hard to view text bigger or smaller than that;only so much can be put on a webpage

Answer 2

headings are used for web page indexes. although the page should be well structured, yet too many levels of headings may be confusing.

Answer 3

might be confusing

Answer 4

Because you don't need more headings, it is just to mark a title of a content.

<h1>-title
<h2>-subtitle
<h3>-...
<h4> - ...
<h5> - ...
<h6> - ...

the font size of the tag you can change with the css